Kubelik NOS DAC kits

[kp93300]

These are the voltage
Across R2 is 0.567v
R66 . 565v
R57 is 0. 606v
R58 is 0.606v

 

[abraxalito]

No significant difference there between the two channels. So looks like lifting pin6 can't be avoided. Lift one at a time and listen for the static noise disappearing.

 

[kp93300]

I lift up dac pin6 one by one and pproblem persisted.
I notice that the static noise only appear after a few minutes of power on.
I will try replacing some of the transistors involved in current source circuit

 

[nautibuoy]

Hi Richard. I plan to, finally, asemble my Kubelik DAC over the Christmas break - I've had a bit of practice soldering small SMD parts so I'm hopeful!

I will use the DAC in a 'workshop system' so it would be really useful to be able to stream music from my smartphone via Bluetooth - just wondering if you've tried a Bluetooth input using something like this;

https://www.aliexpress.com/item/100...00019017010263!sea&curPageLogUid=MPeFZZ0CBNlE

 

[abraxalito]

Hi Ray - no experience with that particular one, no. We have successfully used this one with a few of our DACs : https://www.aliexpress.us/item/1005...00026463523344!sea&curPageLogUid=VXWRtnmPo1Yb

 

[nautibuoy]

Thanks Richard. I'll give the one I linked to a try, it's in my basket on Aliexpress for when I next place an order.

 

[abraxalito]

Let us know how it goes. Kubelik is low-maintenance as a DAC as it doesn't need an MCK from the source component.

 

[nautibuoy]

Let us know how it goes. Kubelik is low-maintenance as a DAC as it doesn't need an MCK from the source component.

Yes, that was part of my thinking.

I'll post results in due course.

 

[nautibuoy]

I decided to do some more SMD soldering practice today and the result is...

Applied solder paste, placed parts then used my hot-air station - it took a few hours, it looks OK but the proof of the pudding will be in the eating of course.

 

[nautibuoy]

Today I ordered the bluetooth i2s module from Ali Express.

In the meantime I started to put a 20V power supply together and can use a JLSounds USB board for an i2s source so hope to get a listen to my Kubelik in 2022.

 

[nautibuoy]

Hooked it up to a power supply today, all the voltages checked out...

So I completed assembly of my Kubelik - just have to wait for the Bluetooth receiver to arrive now.

 

[kp93300]

Back from holiday.
Start afresh to troubleshoot.
These are readings today.

 

[abraxalito]

Are those readings with I2S playing into the DAC? The U8 opamp seems to be working fine (its + and - inputs are at the same voltage) but there is an offset at the output which seems larger than normal DAC operation would expect (between +7V and +13V at TP7). The offset could be from the current source transistors (Q17,Q19) not functioning correctly.

 

[kp93300]

i2s is not playing when these measurements are taken.

 

[kp93300]

I also noticed that there is now a constant humming sound and U8 runs very hot quickly

 

[abraxalito]

TP5 is showing a serious fault condition at 18.8V - its worth checking that R37 doesn't have any voltage drop across it. If it does, that would indicate a failure of the MOSFET Q14. U8 running hot is a significant concern - check its output current by measuring volts across R32 and R63.

 

[kp93300]

TP5 is showing a serious fault condition at 18.8V - its worth checking that R37 doesn't have any voltage drop across it. If it does, that would indicate a failure of the MOSFET Q14. U8 running hot is a significant concern - check its output current by measuring volts across R32 and R63.

When powered up, no voltage across R32, R63 and 37.
I noticed that the markings on R66 appears faded

 

[kp93300]

Notice faded marking on R66.
What's R70, SOT in the schematic? . I left it blank, unpopulated on the board

 

[abraxalito]

R70 is for tweaking the DC offset, which is optional. You could measure voltage across R66 (or R70 which is in parallel) to check that the current source is behaving as expected. Also worth checking that R66 is still 120ohm.

 

[kp93300]

Happy New Year to Richard and all users of Kubelik.
I am happy to report that the dac is working as expected now.
I replace R66 and this solves the overheating of U8.
I replace Q28 and the voltage at TP5 is within specs.
I measure all the TP voltage after these 2 changes. All measurements within spec.
Testing for about 1hr of usage, everything is good. No hum or distortion.
Thanks to Richard for first rate support!